1. Field of the Invention
This invention relates to a plunger pump wherein an inlet valve and a discharge valve are operated by a reciprocable plunger to feed a predetermined quantity of fluid under pressure.
2. Description of the Prior Art
Heretofore, there have been utilized plunger pumps of various types for feeding various fluids such as coating composition including paint under pressure. With these plunger pumps, when the pressure-fed fluid is inorganic paint, zinc rich paint being in the form of slurry and including therein solid tramp materials and the like, such disadvantages have been presented that these paints tend to wear slide portions of the plunger and deteriorate the lubricating properties, thus rusulting in an unstabilized operation.
In view of the above, such a plunger pump has been developed that, in a plunger pump for a zinc rich paint and the like, for the purpose of protecting a slide portion between a plunger and a plunger case, a bellows is provided between the plunger and the plunger case to thereby completely separate the slide portion of the plunger from the zinc rich paint which is a pressure-fed fluid due to the presence of the bellows (Refer to Japanese patent application publication No. 2721/1977). However, with the plunger pump of the type described, in which the pressure-fed fluid flows through the plunger, the pressure-fed fluid should necessarily pass through the interior of the bellows. Consequently, when the pump is disassembled to be cleaned after use, unless the bellows is entirely removed, the paint and the like contained in the bellows cannot be removed, and further, a pair of bellows are provided at opposite ends of the plunger, respectively, due to the construction for allowing the pressure-fed fluid passes through the interior of the plunger, whereby it takes long period of time, as a whole, after use, thus presenting such drawbacks that the operation is performed at a low efficiency and the provision of the pair of bellows and the like results in increased costs of manufacture.
Further, in the plunger pump described in the aforesaid patent application publication No. 2721/1977, oil used for countering the pressure of the fluid fed through the bellows under pressure is filled in a space formed between the bellows and the plunger case. However, to prevent the bellows from being deformed to a high extent, the pump is designed such that the inner diameter of the plunger case is substantially equal to or slightly larger than the maximum diameter of the bellows. Because of this, air foams mixed into the oil while the oil is being filled into the space formed between the outer peripheries of the bellows and the inner periphery of the plunger case, tend to be held between respective ribs of the bellows and it is very difficult to remove these foams, whereby a pressure ballance between the interior and the exterior of the bellows may be lost due to the presence of these foams, which possibly leads to damages of the bellows.
Consequently, it has been indispensable to remove the foams from within the liquid such as the oil for countering the pressure of the pressure-fed fluid, and, heretofore, a special filling apparatus has been required for filling the liquid, thus necessitating to perform a very troublesome filling operation.